The present invention relates to an electrical energy storage system for traction power supplies, and more particularly to a system used to capture excess power detected on a traction power supply (as a braking recuperation system) and/or release some power to the traction power supply when power is in demand (as an acceleration assist system).
It is known in the art to provide an electrical energy storage system (ESS) to assist regulating the traction power supply (TPS) of a light rail network or the like using electric dual layer capacitors (EDLC) commonly called ‘super capacitors’ connected via a bi-directional DC-DC converter power supply. However, such ESSs have limited capabilities to take advantage of the full storage capacity of the different EDLCs due to the rapidity of the high voltage direct current (HVDC) transfer required as well as the management of any abrupt power transfer rate due to the ESS storage bank approaching an upper or lower boundary voltage condition. When the TPS voltage falls below an acceptable low voltage threshold, it is essential that the ESS can provide the required additional power to the TPS, and reversely, when the TPS voltage exceeds an acceptable high voltage threshold, it is essential that the ESS can recuperate the excess of power on the TPS line as quickly as possible, considering that excess energy found in the TPS (at a voltage level above the upper threshold) is typically directed to a load for elimination thereof in heat by the TPS itself.
Accordingly, there is a need for an improved electrical energy storage system.